Honda FRC800 Manuel Du Propriétaire page 48

SERVICING YOUR TILLER
6.To adjust, loosen the four engine mounting bolts and the two belt
stopper attaching bolts (front side), and move the engine forward or
backward to get proper tension on the belt.
ENGINE MOUNTING BOLTS
During adjustment, line up the groove of the engine-side pulley and that of
the transmission-side pulley. If they are not aligned, the belt may come off
or will wear prematurely.
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ENGINE-SIDE PULLEY
BELT STOPPER ATTACHING BOLTS
TRANSMISSION-SIDE PULLEY